When should I upgrade the DB to Multi-Pub?

Here’s a silly questions but does any one have advice on when I should upgrade my db infrastructure into multiple DB’s.

Currently I am on grid computing which by definition has multiple db’s. I find that page load is sometimes delayed which I think may be db based.

I currently have 2 core Blogs with 5k pv a month with a goal to grow this to 100k by end of year.

I will be rolling out about 3 other sites that will have roughly 30 – 50k by end of year.

Advice is much appreciated.